1. Field of the Invention
The invention relates to a method for oligomerizing straight and branched chain olefins having from 2 to about 12 carbon atoms by passing such olefins over a ZSM-12 zeolite.
2. Description of the Prior Art
It has long been known to contact various hydrocarbon fractions with acidic catalysts generally and, in particular, with solid siliceous acidic catalysts--including those referred to as crystalline aluminosilicate zeolites. Contact of hydrocarbon feeds with such acid catalysts is carried out for a wide variety of reactions, including cracking, isomerization, hydrocracking, etc. Representative U.S. patents disclosing and claiming contacting various hydrocarbon fractions with crystalline aluminosilicates are U.S. Pat. Nos. 3,140,249; 3,140,251; 3,140,253; and 3,140,322.
Oligomerization and polymerization of olefins in the gas phase over various zeolites such as Linde A, X and Y is also known to the art. A major problem associated with such reactions is the formation of very high boiling hydrocarbons which remain on the catalyst and block the active sites. This causes rapid aging of the catalysts.
Conversion of C.sub.2 to C.sub.5 olefins over ZSM-5 catalysts is also known to the art. In U.S. Pat. No. 3,960,978, a process for producing a gasoline fraction containing predominately olefinic compounds which comprises contacting C.sub.2 to C.sub.5 olefins with a ZSM-5 type crystalline aluminosilicate zeolite at a temperature of from about 500.degree. F. to about 900.degree. F. is disclosed. In U.S. Pat. No. 3,827,968, a two step process comprising oligomerization of a gaseous C.sub.2 to C.sub.5 olefin containing stream by contacting with a ZSM-5 type of zeolite at a temperature of from about 550.degree. F. to 850.degree. F. followed by aromatization of the product of the oligomerization reaction is disclosed. The processes disclosed in these patents differ from that of the present invention in that they employ a different catalyst and higher temperatures.
Zeolite ZSM-12 and hydrocarbon conversion over ZSM-12 are disclosed in U.S. Pat. No. 3,832,449 and U.S. Pat. No. 3,970,544 respectively. In U.S. Pat. No. 3,775,501, a process for the production of aromatics which comprises passing a mixture of air or oxygen and a hydrocarbon having from 2 to about 16 carbon atoms over a ZSM-12 zeolite at a temperature between about 500.degree. F. and 1300.degree. F. is disclosed. These patents do not disclose the oligomerization process of the present invention.
In U.S. Pat. No. 4,021,502, a process is disclosed in which gaseous C.sub.2 to C.sub.5 olefins are converted into gasoline blending stock by passage over ZSM-12 at temperatures of from about 450.degree. F. to about 1200.degree. F. The process disclosed in this patent differs from that of the present invention in that the process of the present invention utilizes temperatures much lower than those disclosed in the patent.